Inhibitors of protein kinase C selectively enhanced leukotriene D4-induced calcium mobilization in differentiated U-937 cells.
U-937 cells differentiated with dimethylsulphoxide for 3-4 days express receptors for leukotriene D4 (LTD4), which are coupled to Ca2+ mobilization and phosphatidylinositol (PI) metabolism. Treatment of U-937 cells with an inhibitor of protein kinase C (PKC) [staurosporine (100 nM)] augmented the Ca2+ mobilized by LTD4. The peak concentration of the LTD4-induced increase in [Ca2+]i was 1500 nM in untreated cells and 3000 nM in cells treated with staurosporine for 30 s. Maximal mobilization responses were observed at 1-10 microM LTD4 in both control and staurosporine-treated cells. The increased Ca2+ response to LTD4 after staurosporine treatment occurred within 30 s and was attributable to both intracellular and extracellular stores. Additionally, a second phase of Ca2+ mobilization occurred after stimulation with LTD4, which was elevated by pretreatment with staurosporine--this effect was maximal after 5-10 min of treatment. Staurosporine either had no effect or decreased the Ca2+ mobilization response of differentiated U-937 cells to other agonists, such as LTB4, platelet activating factor, ATP or the chemotactic peptide f-Met-Leu-Phe. Although staurosporine alone had no effect on basal PI metabolism it increased LTD4-induced PI metabolism. Staurosporine did not prevent the tachyphylaxis observed upon second challenge with LTD4, nor did it prevent LTD4-induced homologous densensitization. Other compounds which inhibit PKC (sphingosine and 1-O-hexadecyl-2-O-methylglycerol), also enhanced the Ca2+ response of U-937 cells to LTD4, but not to other agonists. These data show that inhibition of PKC enhanced responses of LTD4, suggesting that PKC plays a role in determining the responsiveness of LTD4 receptors.
Winkler
J D
JD
Department of Pharmacology L-532, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406.
Sarau
H M
HM
Foley
J J
JJ
Crooke
S T
ST
D000470:Alkaloids / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D013189:SRS-A / Q000494:pharmacology*; D019311:Staurosporine
D000470:Alkaloids; D007295:Inositol Phosphates; D013189:SRS-A; D011493:Protein Kinase C; D019311:Staurosporine; D002118:Calcium; D004121:Dimethyl Sulfoxide